Transport networks are known to have the capability of providing dynamic recovery mechanisms able, in case of failure, to protect the traffic. In particular, the protection is provided within a short time frame.
Many wavelength division multiplexed (WDM) control plane implementations are based on distributed signaling and a centralized Path Computation Element (PCE). As soon as a failure occurs, the ingress nodes of the optical Label Switched Paths (LSP) impacted by the failure ask the centralized PCE for the computation of an alternative path. The communication between the ingress nodes and the PCE is an extremely critical issue, as a delay in the communication between them highly impacts restoration time.
For optical LSP, a signaling protocol of a control plane can be used by ingress nodes to set up a protection path. This requires use of a signaling protocol.
Packet networks (e.g. IP/MPLS) are able to provide pre-provisioned protection schemes (e.g. Fast Re-routing—FRR) where forwarding tables can be preconfigured and, in case of failure, local protection decisions can be made depending on the header of the incoming packet.
FIG. 1 shows a prior art example of local recovery in a packet switched network 100. Packets 110 include identification data in the Internet Protocol (IP) packet overhead or in a multi-protocol label switching (MPLS) label 111 to inform nodes crossed about the destination of the packet. In particular, for a label switched path (LSP), the packet label 111 informs all the nodes crossed about the destination of the LSP. In this case, a primary LSP 102 originates at node A 122, then node B 124, node C 126 and terminates at node D 128. Nodes B and C 124,126 can be configured to provide local protection to the packet network (e.g. IP/MPLS). In the example shown, a link B-C 103 between nodes B and C is broken. Node B 124 is configured to send the traffic towards node F 132 along a protection path 106.
The node B is configured to apply a different label to indicate the alternative path. The packets are forwarded to node G 134 and then to node C 126 using the alternative path label. Node C 126 is configured so that incoming traffic with the primary (working) path label 102 and incoming traffic from node G 134 with the alternative (detour) path label 106 are handled in the same way, in particular, forwarded to node D 128 with the primary path label. The packet header 111 can contain the label for the primary path 102 and the label for the alternative path 106. Only the outer label is used for switching, such that the label for the alternative path 106 is exclusively used on the alternative path. Switching can be carried out with the same procedure on both the primary and alternative paths, with the labels read from a header. The label for the alternative path is then removed from the packet. Lambda-switched optical transport, for example, cannot add an additional label in this manner.